This invention relates to radiation detection devices and, more particularly, to a system which sums up the individual intensities of certain elemental constituents in a sample from a plurality of detectors and utilizes the summation as a material sorter or as an intensity input representative of density to compensate an X-ray thickness gauge for changes in composition.
Radiation detection systems have been utilized to identify elements in a sample, e.g. radiation spectroscopy, and to identify physical characteristics such as thickness, e.g. X-ray gauge.
The basic requirements for spectroscopic measurements are a radiant-energy source, a dispersion device and a detector. The source emits either all the wavelengths within a range or the wavelength which is to be measured. The dispersion element separates the radiant energy into its various components at different wavelengths and the detector measures the relative intensity of the radiant energy at those wavelengths.
A physical measurement can also be made through X-rays. For example, the process of rolling or forming metals and nonmetallic materials to a given thickness is often controlled by an X-ray thickness device which operates by passing a beam of radiation, of a predetermined wavelength, through the material with the transmitted portion of the radiation being detected by various radiation detection means. The density of the material is reflected in the amount of radiation absorbed. Therefore, calibrated thickness of material with the same chemistry permit the construction of a plot or curve from which unknown thicknesses can be determined.
The absorption coefficient of a material is a function of its composition. This is true because each element of the material has a specific atomic weight which correlates with its physical density and the density has a relationship to its absorption characteristic for a particular wavelength of radiation.
The signal from a radiation detector such as an X-ray gauge can be fed forward to cause changes in roll spacings, pressure or drive speed to maintain the desired physical thickness of the product. Should the density change, due to a change in composition, the transmitted beam will be erroneous as to a given thickness measurement.
Certain types of composition compensators for thickness measurements are known. Exemplary of these are U.S. Pat. Nos. 3,482,098; 3,210,545; and 2,988,641. It is also known that more than one element or more than one parameter can be detected at the same time through X-ray radiation techniques. Exemplary of those teachings are U.S. Pat. Nos. 3,046,399 and 3,489,901.
It is an object of our invention to obtain a signal representative of certain critical elements in a material and utilize that signal to either identify that material with respect to other similar materials and/or to compensate an X-ray thickness gauge for changes in composition in a material or from material to material.